This invention related generally to the field of animation, and more particularly to a method for approximating the lighting of a 2-dimensional animated image.
For more than 80 years, artists and film makers have attempted to blend 2-dimensional (“2-D”) animation and 3-dimensional (“3-D”) live action scenes seamlessly in movies. High points in the integration of the two media include the Fleischer Studio's “Out of the Inkwell” series in the 1920's, MGM's “Anchors Aweigh” (1945), Disney's “Mary Poppins” (1964), and the Disney-Amblin co-production “Who Framed Roger Rabbit” (1988), as discussed in C. Solomon, Enchanted Drawings: The History of Animation, Knopf, New York (1989). In each case, the artists utilized, and often invented, the most sophisticated technologies available at the time, for example, the rotoscope, the sodium/blue-screen, traveling mattes, and optical printing. Currently, artists use 3-D computer graphics (“CG”) tools to design and create new animated characters, however, the use of 3-D CG tools to recreate drawn characters faithfully has proved expensive and often ineffectual.
The primary components used to illuminate a point on a surface of an object in 3-D are its position and surface normal. In hand-drawn artwork, the surface normal is unknown, and the position information lacks depth. Previous work completes the data through geometric methods—creating a 3-D surface from 2-D information, as discussed in T. Igarashi et al., Teddy: A Sketching Interface For 3D Freeform Design, Computer Graphics 33, Annual Conference Series, 409–416 (1999); or fitting a 3-D geometric model to the 2-D data as discussed in W. T. Correa et al., Texture Mapping For Cel Animation, Computer Graphics 32, Annual Conference Series (Aug.), 435–446 (1998).
Systems like Teddy (see previously mentioned Igarashi et al.) and SKETCH, discussed in R. C. Zeleznik et al., SKETCH: An Interface For Sketching 3D Scenes, Computer Graphics 30, Annual Conference Series, 163–170 (1996), provide interactive tools for building 3-D models from 2-D data, automating the “inflation” of a 2-D image to 3-D geometry. In L. Petrovic et al., Shadows For Cel Animation, Proceedings of SIGGRAPH 2000, ACM Press/ACM SIGGRAPH, Computer Graphics Proceedings, Annual Conference Series, ACM, 511–516 (2000), these ideas are expanded and applied to existing drawings to create shadows for cel animation through derived geometry. Also, in W. T. Correa et al. (see above), existing geometry was taken and deformed to match cel animation for texturing and illumination purposes. More recently, sparse interpolation has been used for image reconstruction in lumigraphs, as discussed in S. J. Gortler et al., The Lumigraph, Proceedings of ACM SIGGRAPH 1996 30, Annual Conference Series, 43–54 (1996).
The above geometric methods provide useful results and can work well for integrated 2-D/3-D pipelines. However, these geometric methods work best when the images are less fluid, and, thus are less efficient for “cartoony” animated images, where the addition, removal, or modification of a few lines can alter the geometry of the image. Accordingly, there is a need for a method for efficiently illuminating a 2-D animated image without having to establish the depth of the image. The present invention satisfies this need.